(1) Field of the Invention
The present invention relates to a cable deployment system and, more particularly, to a hydrodynamic cable deployment system suitable for deploying a cable tether between a sea vessel and an expendable device launched therefrom.
(2) Description of the Prior Art
Expendable devices are commonly deployed from underwater vessels wherein a wire communications link is maintained therebetween via a cable tether. When such tethered expendable devices are deployed, the communications link, as for example, a fiber optic cable, which is connected to both the launch vessel and the expendable device, is rapidly stripped away from a coil of cable stowed within the launch vessel and/or within the expendable or non-expendable device by a process called "paying out". Specific examples of applications for cable tether deployment systems which have been investigated by the U.S. Navy include fiber optic tethered torpedoes and tethered communication buoys.
In the fiber optic tethered torpedo application, the cable tether is payed out from coils of fiber optic cable housed in both a submarine and a torpedo such that the deployed portion of the cable tether is substantially stationary in the marine environment. Since launching a torpedo is an inherently high-speed operation, excessive stresses are exerted on the cable tether during the pay out process such that the fiber optic cable must be strengthened to avoid fracture or breakage of the cable. This requirement for strengthened fiber optic cable necessarily increases the cost of the torpedo deployment system.
In similar manner, the tethered communications buoy application involves the pay out of cable at both the buoy and typically a submarine. The cable is payed out at the submarine via a lifting body which houses the coil of cable and is towed above the submarine during cable deployment. In this application, the communications buoy and lifting body are launched in unison from a signal ejector tube on the submarine, the ejector tube imposing a limit on the overall size of the buoy/lifting body apparatus. Although this pay out process is not a high-speed operation and does not exert excessive stresses on the tether cable, it would be advantageous to stow the coil of cable within the larger confines of a submarine, thereby permitting the use of a greater amount of cable and enabling the communications buoy to be tethered to a greater distance. The tethered buoy presents an additional operational complication in that the lifting body becomes very unstable in the marine environment during cable pay out due to the fact that the center of mass of the lifting body varies as the cable from the spool is depleted over the pay out range. Thus, further advantages can be realized by housing the coil of cable onboard the submarine so that the lifting body will have a constant center of mass and can be made to be lighter, smaller, and simpler. These modifications reduce the cost of the lifting body and make more space available in the signal ejector tube for providing performance enhancements to the communications buoy.